You will have to super-vet the piss out of those Reps to hit the repair cap if only using 2.. Though it can be done

Personally, for UK line I'd make 3 elite Reps and 7 rolled engies with a good base in Repair as well. All 7 engineers and 1 rep +1 scout pilot in the support slot and 2 reps in the T-slots. Using elite Engineers will make it harder to reach the repair cap as their base Repair is low. All my engineers are 11rep/11engine (restore doesnt matter) except for the rare 11rep/12engine I rolled out.

Unless you want to use AA or PHH in the t-slots then you can only do 3 reps/5 engies/1 scout or 2 reps/6 engies/1 scout in the support slots. But typically for UK, 3 reps, 7 engies and 1 scout is the best support set-up as hardly anyone uses AA on UK BBs and the repair rate is blistering fast.

+1 ^^
make sure if your going to use 2 reps only. that you roll your engies with a base stat of at the very minimum
11 engy
11 repair
11 restore

(if you can manage 12 rep, 12 engy that would obviously be better)

you will need 200+ vets on those reps and engies to hit the repair cap at normal level (in the 80's)

UK/US go with 3 reps and fill in the rest of the supports with engies. you will still hit the speed cap and have excellent OH duration and good rep speed and you wont feel the need to spend retarded amount money trying to vet the sailors to 160+ unless you want to. with the 7/3 setup you can manage comfortably with 110-130 vets on the supports.

MN/KM/IJN you will want 4 reps the rest of your supports engies some do with 3, but i dont recommend this as these 3 nations suck at repair speed

SN i have no idea, but from what i have seen is similar to US/UK

as for the original question... beyong level 85 or so, a restorer is pretty much useless as the rest of the crew are pretty much doing jobs efficiently and the restorer is no longer aiding in essentially picking up the crews slack... after level 85 or so the restorer essentially gets fat and lazy, gets drunk all the time, pisses of the rest of your crew and just takes up space that can better served with an engy or rep

Hmm, some info that isn't all that correct:

First; with only 2 repairers to hit the rep cap you'll need engineers with 11+ repair, needing 11 restore is BS, and you'll still need to overvet everything to a pretty high standard. And you won't hit ever hit the rep cap in the 80's, only with a crew with a redicilous amount of ebve reps would you ever do that.

Second, US repair rate is not on a par with the UK repair rate and never will be. So expecting to use the same amount of US reps as UK reps and then saying that the repair rate is even close to UK is just wrong.
No chf repairer promotion and no +2 rep stat for every sailor just make that impossible.
A 7/3 setup might hit the rep cap for UK with the 110-130 vets( I don't have the numbers on it atm), but I have very big doubts whether a similar US setup will, wouldn't suprise me if you needed a significant extra amount of vets to even come close.

If you were to use a fixed number of engineers and repairers across all nations, UK repair rate is way ahead. IJN/US/MN make up the following group, IJN actually being the 2nd best repairer by a very small margin. KM and SN are slightly behind those three because their engineers contribute less to repair rate.

But back to the OP, Yes a Restorer is a waste of space, when you hit 900SD without him, you wish you had levelled an engineer or repairer instead

Hence the reason why i keep a restore on muh L2 for when im havin a bad day and get beatin to a pulp i can run away and come back almost brand new into the fight

Except you reach that point at 900 SD, so a restorer is still useless, unless you need to fill a support slot with a very bad repairer.