Actually, the Sea&Sea MX10 is only rated to accept ISO 100 -or- ISO 400 film...
If you're looking for color print film only, I agree with Dee about Fuji Superia Reala 100 - it really is the best consumer 100 print film (NOT Fuji Superia - but Fuji Superia "Reala" as they are two different films).... Also good are: Kodak Royal Gold 100 - but it's soon to be discontinued... Kodak Professional Supra 100 is a good print film - and can be bought in "pro packs" at a reasonable price... Konica Centuria Super 100 is supposed to a SUPER print film - but I can never seem to find it.
When you move to a faster speed film - you'll be adding some "graininess" to the prints. However, you might try Kodak Professional Supra 400 as it has very fine grain, greater enlarge-ability, and vibrant colors... Once again, these can be bought in "pro packs" of 20 rolls for under $50.00 on-line at B&H.... You didn't say which Fuji 400 print film you were using (Superia -or- Press -or- NPH), so I can't be of much there...
Also slide film has LESS latitude than print film, so your exposure has to be "right on" to achieve a decent picture... If you do decide to move to slide film, I would suggest Kodak Elite Chrome Extra Color 100 (EBX)... It's the ISO 100 slide film of choice for my housed SLR outfit.