The XP DS1015 seems quite decent - brushless and speed about 0,1 sec @ 60 deg. It exists in two versions though, at the end of this post, there's a copy of features/specs.

Anyway, I think I read somewhere that the KO TX's require KO RX + KO servos to get the ultimate response. But I'm no expert about this, so I suggest that you dig into the details, before deciding - total budget for servo, eventually extra RX's and TX might be a factor too

Specs & info from www.cmldistribution.co.uk :

Available in two versions, Team Associated’s XP Digital Servos feature many enhancements that improve vehicle control and on-track performance. Equipped with an all-new ultra-precise metal gear and an advanced microprocessor, the XP Digital Servo provides precise outputs and ultra fast signal response. The state-of-the art aluminum heat sink mid case lowers operating temperatures for fade-free performance.

Features

Water and dust resistant
JR type connector
Aluminum heat sink case
Coreless motor
Equipped with ultraprecisemetal gears

Advancedmicroprocessor that processes signals faster and with
more precision

Advanced case design enhances structural integrity
Higher holding power with fewer angular errors
Superior torque output with low current consumption


Spec Check
Dim. (LxWxH)mm: 41.8 x 20.6 x 39.6
Weight (g/oz): 66 / 2.328
Torque (Kg-cm/oz-in) @ 6V: 14.5 / 201.4
Transit Time (sec/60°) @ 6V: 0.108
Voltage Range: 4.8 – 6V