One complaint I had when attempting to mix modern Shimano levers (RX100) with older centerpulls (Weinmann) was that the return spring in the levers made the braking effort harder overall. (SLR levers were designed for brake calipers with weaker springs.) This can also be a problem when mixing modern brake levers with older caliper brakes, as I found on my gf's Peugeot project.

I was much happier when I switched to older brake levers that didn't have the return spring. Braking from the hoods isn't as nice, but I ride mostly in the drops anyway.