Not keen on the weight of the pluses! I like the idea of taking this one along tracks and stuff, in which case the current tyres are probably fine, but I know I'll end up mostly on rough roads, country lanes and the hard pack canal paths. So something a little thinner and more road oriented I think should be ok.
I'll try what I've got some more first, the Supreme's aren't cheap so not likely to suddenly order a pair!
Aye, the Pluses do weigh a ton.
Another thing to consider with your nicely close fitted mudguards is clearance.
Any new tyre will have a slightly different profile.
While there looks to be some room on the bike to adjust the mudguards, I can tell you it's the least favourite job in the bike shop because it's a faff to get right.
My change from Supremes to Pluses nearly hit the buffers, the rear is a shade too close to the mudguard and there's no tinker room because the guard is hard up against the underside of the rack.
I didn't see that coming, particularly as I went from 2.00" Supremes to 1.75" Pluses.
As regards cost, I've found Bike Discount to be good for Schwalbe tyres.
The website is not the easiest to navigate, but have a root around here:
http://www.bike-discount.de/en/shop/non-folding-tyres-250/l-24/o-hersteller