"Modern" laptops are not flexible enough for Windows 9x Although you're comparing apples to oranges. That Pentium can use DOSBox and run circles around 486, specifically in some heavy Build games like Blood.

What motherboard is your Pentium? It likely needs a new coin cell battery or the Dallas clock replacement.

Not all Win9X games work well on XP, and later-era DOS games will run much better with a more powerful machine.

You could just use DOSBOX, but then why have the 486 either?

coin cell already chenged simply all time boot it asl me for the data entering the bios. error 161 and 163.

i not want to use dosbox, only real hardware

Depends on the games more then anything else.
If your games are known to have good XP compatibility and aren't very demanding on the GPU, RTS's for example then no need of a 9x box.
3D titles may be held back by the onboard GPU, only one way to find out, try!

Late dos is where I also see biggest gap in this setup. but if your 486 plays all your dos games fine then no problem either

I'm not a big fan of 3D games like Tomb rider or unreal, like 3D games I just need screamer and doom1 / 2. Then I am much more fond of games like command & conquer, dune2 etc.

Could a pentium 4 even without isa make up for this gap?

It all depends on the games you want to play, but my feelings is that a Pentium 200/233MMX or a K6-2/3 is able to handle most of the last speed sensitive games. POD having an upper limit of a 233MMX is an example. The MMX and K6-2/3 also allow downclocking to larger ranges than what you can get from a 486 66 or 100.

For my personal machines I have a P233MMX for DOS, Athlon64 with Win98, and i5 for XP. I've been able to play everything I've wanted.