Although rod-to-stroke ratio will not significantly impact the combustion to the extant you are suggesting strad, it most certainly have an effect. In reality it is likely to cause no more than a degree difference in how the pressure pushes the piston down.
The most significant impact of rod to length ratio is how it draws the air into the cylinder. It's been uite a long time since i've done this, but longer Rod:Stroke ratios will suck better after 90aTDC (that is better than a shorter R:S ratio, not it acutally sucks harder over the whole cycle). Shoter rod to stroke ratios suck better between TDC and 90aTDC.
It will also affect mean piston speed. I have the 'dwell' profile calcualted.
1/Z is the rod to stroke ratio (please not I think I messed up and labelled this graph wrong, the blue line should be 1/Z = 6). The greater the Rod to stroke ratio the closer to sinusodal motion you get.
This was from an analysis I did on a vintage Austin 7 engine, looking to matte two blocks to form a V8.
As you say Strad, the key is to get a pressure peak as late as possible without losing overall work. As this means that more pressure is going to make torque, and less is going to bend the crank.
However it's also interesting that this becomes largely meaningless at high RPM, as the torque output is determined by the inertia of the crankshaft.
Here is an image of how the inertia and gas pressure forces combine to give the overall force acting down the cylinder axis. I belive this is a graph of 1500rpm.
I don't have an inertia dominated graph available currently, but i'll try to upload one later when I'm back home.