This seems a bit unfair to those who have to wait months for their +100% investments. The speed of the +5% investments should be maximum 14 times the speed of the +100% investments, because of the compounded interest effect:
2=1.05^x => x=log(2)/log(1.05)= 14.2067...

And you should also consider that reinvestment of those 5% things causes a lot of extra transaction fee...
So if there is potential to speed things up, i vote for prioritizing the 200% investments.
Of course I will go with the 5% investments when my calculations conclude this would double my money faster, but this seems like a waste of transaction fees.

And a suggestion: How about automatic reinvestment or the option to only pay out dividends (until I press a cancel button or smth)? Lets say I invest 10BTC, your site doubles it, sends me 10BTC and continues the doubling process with the other 10BTC.