There is a massive improvement everywhere but I did the job at the same time as getting some bigger chambers on and mending the pv (that was broken and stuck in closed position) also it's only now I have the 38mm mikuni's on without the pv broken so who knows really without just swapping that one thing over and doing back to back runs (something hard to find the time/money for). With the rgv the reeds open very close to the pistons and this is worse on the 300 overbore. In fact on the top cylinder the reed stops partially block the boost port due to things being very tight (though this is simple to cure). The rgv is known to have low crank volume and my thinking is that the 300 makes this worse and that having the extra volume near to the transfers is a good way of reducing crankcase compression. I do feel I have some scope now to reduce the combustion chamber volume slightly to get back to an optimun final compression ratio (for pump fuel) but I don't know by how much and as the Stan Stephens 300 conversion already uses oring head I can't play around with head gasket thicknesses though I have a few spare heads!!!
IMHO the nsr looks a better bet for 300cc than the rgv (notwithstanding reliability issues) and if I was looking to get a 250 stroker with 300cc in mind then the nsr150 barrells make the nsr the better starting point, but that's not how we actually do things anyway is it. I can't see my overbored rgv motor ever making 74bhp though 70 might be on the cards one day. Hindsight is a wonderful thing but what counts is what we learn and the fun we have along the way.