I made the Structural Integrity Field stronger than usual for this size vessel because she can make planetfall. It is probably easier on a Nova than a (much) larger Intrepid, but I figured that they would still go on the side of caution in this. The Intrepid (Size 6) has a 6 and the Defiant (same size) a 7 in the SRM (but the SIF is mentioned as being important to keep the ship together at high warp, but it is still 2 levels higher), so I thought it was more in line with those vessels that have planetfall capacity.
Re: Security rating. Honestly, I don't know why I made it so strong; I did this version of the ship some time ago and only posted it because of the request. I did tweak some other numbers, but this one slipped past me to be honest. Having the security that high doesn't seem particularly 'right' to me at the present moment, although it could be justified if the Uprated vessel were used for courier missions (the Warp 8 max Nova would be useless in that capacity) or something. Maybe any ship with Holocommunications Ability and Holoemmitters on every deck (because of the higher EMH in the uprated) should have greater security to prevent hacking into the system? Overall, it makes the system something like 6 SU more expensive, but I do get your point that it still doesn't overly fit. If I do a major overhaul of the ship's stats, I probably should revisit this, otherwise it isn't particularly problematic.
"If you haven't got anything nice to say about anybody, come sit next to me."
- Alice Roosevelt Longworth