I own and love speakers that conform to the BBC design philosophy (Harbeth, Spendor, Stirling) and recently bought a pair of Magnepan .7s. With a decently powerful amp (like your Hegel), these Maggies offer the best value of any speaker I've encountered, especially at U.S. prices. The .7s actually produce more bass than most speakers the size of C7ES3s.
I've also owned the Maggie 1.7is but didn't like them nearly as much. The .7 is better balanced, with superior cohesion and bass dynamics. Anyhow, if you like the Harbeth sound, I think you'll find acclimatizing to the .7s is easy. Caveats being that they need at least one meter of distance from the wall behind them, the toe-in can make or break their treble balance and their soundstage imaging won't be as "pin-point" as that of your P3ESRs, but they're still better in that regard than the larger Maggies.
I've also owned the Maggie 1.7is but didn't like them nearly as much. The .7 is better balanced, with superior cohesion and bass dynamics. Anyhow, if you like the Harbeth sound, I think you'll find acclimatizing to the .7s is easy. Caveats being that they need at least one meter of distance from the wall behind them, the toe-in can make or break their treble balance and their soundstage imaging won't be as "pin-point" as that of your P3ESRs, but they're still better in that regard than the larger Maggies.