I think I found a bug from UT3 patch 5 (v2.1). When you have installed custom characters like popular X.E.N.O and start hosting public Campaign mode, where all players (= clients) forced use UT3 stocks models, start client loading custom characters with very low speed.

I haven't test if this is not true in "normal" running (My Games etc. folder stucture). I run my UT3 with shortucut parameters: \UT3\Binaries\UT3.exe -nohomedir -nomoviestartup.

Yep, to host Campaign, you need to remove all custom characters folder from your UT3 patch. :-(