I say "completely different plane" because the La7 was a complete redesign... visually similar to the La5, and with the same engine, but a whole new airframe. The La5 was basically a LaGG-3 with radial grafted onto it.
The La5 to me just feels different... maybe it's psychological, I don't know. But I fly it a few days than get into the La7 and the difference is staggering, the speed especially.
Actually the air frame of AH's La5FN is virtually identical to the La7. Almost certainly the performance figures used are for the 3 tank metal spared La5FN of late 43 thru 44. (La5FN stopped production in Oct 44..they had to use up spare wings which did not have the air intakes)
It was the metal spared wing that was used for the La7 (lighter than the wooden spar used by early La5FN's and most of the La5F's) plus streamlining the air intake from the wing roots, re positioning and stream lining the oil cooler under and behind the centre tank, stream lining the engine cowlings and exhaust louvres, stream lining the wheel covers, plus a lot of quality control stuff on the panel fits around the engine. The La7 got a 3m prop and slightly longer landing gear...the spinner was slightly modified vis the removal of the hucks dog starter coupling. Some attention was paid to the most efficient use of glue in construction (strength and weight saving) but this was underway with the La5FN also.
Effectively the two planes are historically very similar except the La5FN has more DRAG than the La7.