It's your system specs that is the problem and no that is not the latest version of NullDC but upgrading the version will not help you
If you run in VGA mode it will look very nice on a large screen anyway I run my Dreamcast on a 43 inch TV via VGA, you do not need to make it run any higher than 640x480
Buy a VGA cable or box for the Dreamcast or mod your dreamcast to have a VGA port and enjoy
Some games will need patching for VGA mode to work and there are 16 english games that don't have VGA supported
nullDC v1.04 r150.zip is the latest version, I obviously did not compile that one though, I did not re pack it either with respect to the guy that actually compiled it from the official NullDC source files
The games have nothing to do with it specially as you tested a GD-Rom dump as well, there are some games made into Mil-CD aka selfboot in the past that had issues due to the build of disc but that is in the past if you grab newer builds
Revision notes:-..There are some speed boosts so you may get lucky in the newer revisions.
r150 [Memleaks and misc patches by mathew1800. Closes Issue 477. Closes Issue 478. Thanks. =)] Mar 9, 2013
r149 [audio:nullaica doesn't play nice with the configurable high precision timer(Revert & todo: fixed global timing to 50(PAL)/60(NTSC) ~ 20/16.7ms/frame)] Feb 11, 2013
r148 [release-build-conf:Disable STL exceptions/Disable FPU exceptions/Disable vertifications/Align POD/Struct data/Disable FP generation for a speedup of 10-15%] Feb 9, 2013
r147 stable [renderer:Moved testing code to separate branch renderer:All stable optimization changes have been integrated to the stable branch renderer-naomi:Protect texture cache from unknown/unsupported formats (Fixes crashes in few games)] 2013
r146 [Revert back a mindless change in pvrlock] Feb 1, 2013
r145 [renderer:Prevent textures for being updated more than once per pass. renderer:Rm/ unused code Emitter:Some temporary cleanups/fixes as an excuse for it 'screaming' for a complete rewrite] Feb 1, 2013
r144 [+Impl/ ImgReader MDS/MDF Support] Jan 31, 2013
r143 [*Render state cache : Do not reset single pass states *Texture cache : Do not destroy textures if S0(w,h,bpp) match S1(w,h,bpp) (where S stands for state) but update them. *Do not map/unmap already mapped/unmapped codeblocks +Impl/ sequential_stream] Jan 30, 2013
r142 [+New texture cache manager w/ O(1) find() method +Impl/ render state manager +Impl/ faster sorting method for alpha/z-ordered poly renderer -Removed/Replaced (unused)code *Optimizations for streaming textures *Optimized emu main loop *Tons of fixes/opts] Jan 27, 2013
r141 [Missing return statement in ioctl code ! Fix issue 432 (thanks for reporting !)] Apr 10, 2012
r140 [chd: support for newer format chds arm: read rotates for unaligned, force alignment (fixes audio in some games)] Mar 20, 2012
r139 [pvr/threading tweaked the render timing a bit, further 2-3% speedup on 3d heavy scenes for multicores ..] Sep 13, 2011
r138 [nullAICA/audiosteam: --Improved the way audio sync works, editing some code that called to win32 way too often --moving 1 line around: +10% on speed (from 440 to 485% on my pc ..)] Sep 13, 2011
r137 [(Very) primitive d3d11 renderer: Sets up stuff, draws geometry, nothing much more ..] Sep 13, 2011
r136 [Updated SDL binary. drkMaple: -. Re enable LG LCD (VMU) support by default, again.] Aug 21, 2011