ive literally just done our kkitchen, ok still need to get worktops fitted and tiled...

but id say it depends on where you buy the units from!

ours had an old MFI lot in there, we got the new ones from Wicks, to find that the wall units were not as tall, or as deep as the MFI stuf... of course only knew after i started lol

anyhow, when you take off the old lot, you will be able to see where they were, so if the same size units, hang em in the same place, if not - like me, i fitted to the middle of where they were before lol

good luck tho, my kitchen was a RIGHT pain in the ass! (odd size...)