My 13 Allison (1972) is being restored as I get time, transom, core, the whole shabang. I have a question;

I have an old (1980 ish) 75 OMC, not a nitro-cased motor and it has always been preached to me that it would be best to have a nitro motor, due to the 15 inch mid, as well as, narrower gear case. It is also my understanding that the later 56 inch race motor, is even better, but my question is; if I cannot readily purchase an old nitro motor, or a later racing 56 incher, wouldn't the standard later 56 inch, 70hp motor be better than what I have, and as far as top end goes, wouldn't it also be better than the 49 inch nitro motor, simply because it puts out so much more power?

I am cost consious and not doing any sanctioned racing, but like to go fast. It simply seems that their is no good reason for me to spend $2,000 on a good nitro 49 incher, if i can pretty easily spend, $800 on a good, late 1980's 70hp that is "faster" still, though it will lack the 15 inch, on top end, I see this making little difference.

Thoughts please?