This issue isn’t the end of the world. Luckily Roman armies don’t need much in the way of cavalry anyway. A sensibly sized army will include 2 or 3 units at most. If you want more then you are going to be looking at allied Numidians, Greeks or Spanish. For just a few units the price difference with metals will make less of a difference. There are plenty of choices in 28mm metal Romans that will work well with Victrix infantry. As usual it is a case of looking at all the options and not getting hysterical about what is and isn’t possible to get in plastic.
No, not the end of the world. Personally I always felt Roman Cavalry were not that great at their jobs so I've always gone for Celtic or Numidian cavalry for the bulk of my collection. But if you like collecting miniatures from multiple company's like I do, it seems Victrix is creeping off into their own world of beyond 28mm historical.
As I have said, I love the Infantry Victrix makes.. but I think I'll avoid their Cavalry. Curious to see if their dark age infantry creeps up along with their oversized cavalry.
Are the Victrix Gaul cavalry significantly larger than Victrix Gaul infantry?
No the Gallic cavalry fit in well with the foot figures.
My blog has a few shots of the Victrix Cavalry from both Republican and Gallic sets. I don't have any Victrix celtic infantry since I want to stick with Warlord's, but the cavalry from the previously mentioned two sets are of the same ilk- quite big.
If you do exclusively Victrix miniatures in your army there will be no issue. Don't bring in any Warlord Gauls or Warlord Gallic cavalry alongside Victrix if the oversize worries you! Otherwise, Victrix still makes great models with good details. Just have to be careful if the size differences bothers you.