The listing of COIN will be a liquidity event like no other in BTC history. The most extreme bubble in BTC history is the 53x ramp from April to June of 2011. It would be unreasonable not to consider that the impact of COIN might exceed that event, therefore. A 60x ramp would achieve that by a significant margin, without breaking new territory.
Let's suppose that there is a 50% chance of COIN being listed, and an 90% chance of a multi-month topping formation to ensue, and a 10% chance of that formation, conditional upon its formation, breaking a new scale record. I consider all of these estimates to be low-ball. The resulting contribution to the aggregate value of a bitcoin in Q1 2015, over all scenarios, is 920; a 25 bp/diem return means that if all other scenarios were flat zeros, even so your expection is net 9 bp/diem positive carry against current BFX margin rates.
If the stopping time of a 13% margin call at 620 is less that sqrt((920-620)*9/25) ~ 10 times the duration of the scenario (I take at 160 days), then there is a net negative expectation. I will spare you the stopping time calculation (a bunch of stochastic integration very ill-suited to a forum post). It is much less. In other words, I consider provable given a few reasonable and not very limiting scenario assumptions (although not here proven even conditionally) the (perhaps obvious) conclusion that even the most eggregiously optimistic scenario cannot justify the risk of full margined carry, unless you can get substantially better rates (or higher leverage limits) elsewhere.
Holding, on the other hand, is a no-brainer.
Intermediate leverage falls between, and I have yet to calculate the optimum, which depends on better scenario coverage for its confidence margins. It really requires a numerical approximation to do it on a principled basis with reasonable margins, at my level of understanding. I couldn't expect to produce a closed form for the general case in the time one could allow to do a doctoral dissertation, so it's just not practical for me to try.
TL;DR: HODL
Your posts tend to be fairly inspirational regarding the likely bullish direction of BTC prices.
Currently, I hold more than 100BTC, and I have been very tempted to double or triple my BTC holdings; however, I am a little nervous about such a decision.
I have around $400k in tax deferred index fund accounts (stock market, bonds and govt bonds), and it would be possible for me to make a one-time withdrawal of part or all of those funds, without any tax penalty - though it would likely be a taxable event, unless the funds are rolled into another tax-deferred vehicle. I have been considering withdrawing $150k to put towards BTC... but then I would definitely be less diversified in my total investment package, and I would have a larger percentage of my quasi-liquid assets invested in BTC....
I am pretty confident about the direction of BTC going up rather than down, yet I remain a little uneasy about making such a leap with my quasi-liquid assets and to take such a step.
Over the years, my various tax deferred index fund investments have earned an average of a bit over 6% per year, even though they have been doing better in the last few years - especially after recovering from the 30% decline in 2007. For example, these tax deferred index fund investments they earned more than 21% in 2013, and about 6% in the first half of 2014.
Nonetheless, I continue to lose confidence in holding these various quasi-liquid assets in USD, in part b/c I have additional other less liquid assets in USD, as well. Additionally, as many participants in BTC believe that there are a considerable number of impending problems with USD, especially given the intense levels of quantitative easing that had been occurring, since about 2008 and seemingly ongoing.
It seems that if there are future failures with USD, then those USD failures will be inversely related to BTC appreciation in value. In this regard, it seems more likely that BTC values will double or triple (or even appreciate greater 10 to 100x) in the next few years, rather than my index funds, which could double (2x) in 10-15 years, if I am lucky.
I understand that ultimately these remain personal investment choices that each person has to make based on his/her own risk tolerances, assets and investment timeline.
Get rid of that worthless fiat. Only keep what you plan on spending. You know it is the right thing to do, you explained it pretty well yourself in your second-to-last paragraph.
