Fixed or Variable Rate

Whilst not answering your questions directly, here are a few things to bear in mind.

a) Your analysis needs to take into account the repayment profile of the loan -  fully amortizing over the loan term vs part amortizing vs monthly interest only vs intrest on maturity.     A 3 or 5 year fully amortizing loan, will on average have only about half the capital at risk, or put another way the montly capital repayments can be reinvested at current market rates.

b)  The majority of p2p loans are 3 years or under, with a significant proprtion at 12 months.  Most analysis of future interest rate policy by western governments suggests that whilst base rate rises are now likely in the next 18 months, the sum of the increases over the medium term is likely to be so small as to be largely irrelevant (e.g. in UK best guesses are for 0.25% increases in BBR in spring & autumn 2016).

c) p2p yields are largely interest payments in lieu of future capital losses.  Don't be fooled by the headline rates discussed on this forum, a long term yield after defaults of 6% is probably the best that can be hoped for

d) prior to this tax year, (and the new rules are not yet published for the current year !!) capital losses can not be offset against interest for tax purposes.  The headline yield comes down significantly once (say) 45% tax is deducted on all interest and then capital losses are deducted.   On some platforms the actual net yield for 45% tax payers has been been below BBR (and in some cases negative).  Some lenders use the tax advantages of SIPP/SASS to mitigate this but is only really practical for HNWI's

e) The p2p sector is still in its infancy and yields appear not to be correlated with anything in a meaningful way. On most platforms they are an indication of risk - the further away from say 5% they are the riskier the loan. The forthcoming inclusion of p2p loans in ISA's is likely to bring an avalanche of money into the sector driving down yields irrespective of increases to BBR.