[xubuntu] 16.04 + Radeon HD3450 + 2560x1440 Display, slow 2D/3D acceleration.

I am currently ruing Xubuntu 16.04 on a system which uses Radeon HD3450 as a video card. The system has an inteal graphic processor, but the motherboard is incapable of outputting 2560x1440 resolution (which is the resolution of the monitor attached) so an PCI-e based video card is necessary.

The problem is that 2D/3D acceleration performance is poor, and it fails to handle even simple web browsing fluently. It is even slower than the framebuffer rendering in some cases. I understand that HD3450 is an outdated card and that I must expect some 2D/3D acceleration performance issues, but it is still somewhat slower than what I have expected. Are there any options that I should try changing around before replacing it with a different card? Also, what would be the cheapest graphic card (either used or new) that would give me a reasonable performance on a 2560x1440 resolution? All I need is an usable level of 2D graphic performance (web browsing, video playback, etc).

The graphic card driver used is the default open source Radeon driver for Ubuntu 16.04. Disabling the hardware acceleration support of the web browsers helped, but did not fully solve the problem as the CPU caot keep up with some heavy pages when it is disabled.

Any help would be appreciated.