Matching memory with different timings

I used to have 2x512mb (2.5-3-3- 8 ) ddr ram but one of them a few months ago started giving errors so i took it off. a few days ago i went and got a 1GB ddr ram (3-3-3- 8 ) and installed it. the latency and stuff are auto selected from the bios, when i installed it i went into the bios to see if the settings have changed now that there is an additional stick with slightly different latency. the settings were the same as before and i thought about putting it on manual and putting the value 3 for latency (it was on 2.5) but i first thought to give it a go and see what happens. on loading windows it crashed so i thought about changing the sticks slots just in case. i discovered though that the 1GB stick wouldn't boot any more. i returned it and got my money back thankfully.

the thing though is what exactly did go wrong? i am suspecting that the 3-3-3-8 stick probably tried to run at 2.5 (like overclocked or something), couldn't take it and got wasted. if i had put it manually on 3 though would it have worked ok? is there any way i can match memory with different timings (finding one exactly the same is kinda hard), this is the second time i had to return memory because it wouldn't work with my current stick and i 've started running out of computer shops.