I used to have both 45- and 55-gram Topre 87U keyboards. I did have a problem when going from my 55g to my 45g. The 55g switch has exceptional feel for me; however, I found the 45g lacked feel. Odd as it sounds, when I want a change in key-switch feel after using the 55g Topre keyboard, I transition to a lighter Cherry key switch. Lately, I've been using an MX Red, 45g, KB, which has a completely different feel from Topre's 45g switch. I can also use MX Blue switches for a change in switch feel. However, Topre's 45g, at least for me, has an odd feel when coming from their 55g switch. The 45g feels kind of soft and mushy--it lacks feel, I'm repeating myself, mea culpa.
If you like the 55g switch, stay with it. The reasons I make a change in keyboards are twofold: my fingers tire after using the 55g switch for hours at a time; and at times I simply get somewhat bored with the same key-switch feel (I want to feel the mechanics of a key switch; and when I lose a switch's feel, I have to make a change, which helps [me] to maintain my momentum when writing).
My sense is that you should buy what suits you. And, you may want to note that the feel of Topre's 45g switch is much different from the 55g switch; to me it simply lacks the feel of Topre's 55g switch's properties. My preference, not that this matters, is Topre's 55-gram inside an 87U keyboard. I've never used an HHKB; after buying 45g and 55g 87UBs, the Realforce 55g became my preferred keyboard and topre switch.
Whatever you choose, I wish you the best with your new keyboard, enjoy it.