The slowdown for running Windows in a Linux KVM virtual machine ought to be about 2-5%. I don't know what Flare is -- too many collisions in that namespace -- but unless it is unusually demanding of hardware, I wouldn't expect problems.
I run Debian Linux and the XFCE desktop environment on laptops and desktops, with a variety of screens from 12" 1280x720 to multiple 24" 1920x1200 to 43" 4K. XFCE is very customizable for independently sizing text and interface elements, and my default window titles are cyan on dark gray for the inactive windows, and black on light gray for active. A complete new window manager theme is a few hours work in GIMP, but there are hundreds of existing themes with varying frame widths and title bar heights.
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I run Debian Linux and the XFCE desktop environment on laptops and desktops, with a variety of screens from 12" 1280x720 to multiple 24" 1920x1200 to 43" 4K. XFCE is very customizable for independently sizing text and interface elements, and my default window titles are cyan on dark gray for the inactive windows, and black on light gray for active. A complete new window manager theme is a few hours work in GIMP, but there are hundreds of existing themes with varying frame widths and title bar heights.