If you need analogue-out (VGA) for true low dotclock 15khz emulation, there's nothing above the R7 250 in low profile,
AFAIK.
All you can hope to find is a slightly overclocked model with more VRAM.
Some feature OC and 2GB, XFX even sold a 4GB at some point but they're unicorns.
Not that another 250 will make much if any perceptible difference, methinks.
Otherwise a number of low profile RX series exist(ed), like seen in this article:
http://graphicscardhub.com/best-low-profile-graphics-card/With those because they lack an analogue out, you'll need to add a DAC in your connectivity chain (like an HDMI to VGA adapter) and redo a fitting Groovy settings and modelines installation.
That possibility has been introduced only recently by Calamity, what's an unknown factor is a DAC's ability to pass the modes.