That's what the blank media section of this forum is for People trade information about what media codes match what discs.
I have heard that That's DVD discs are available in certain parts of Greece. I don't know if it is true, but if you can get hold of those, they are definitely Taiyo Yuden discs. The media codes for the 8x version are YUDEN000-T02 (8x DVD+R) and TYG02 (8x DVD-R). These are really good stuff and the media codes will always be the same. Unlike some other brands, That's is the house brand of Taiyo Yuden itself, not some third rate company which buys media from other people and puts its brand on it.
Failing that, you can always get Verbatim 8x DVD+R/-R discs. Those should always be MCC003 (DVD+R) or MCC02RG20 (DVD-R). Avoid Verbatim Pearl tops though - those can be something else.
These two brands are better quality stuff that most people recommend. If you have trouble getting them in stores, maybe you can try buying them from online stores. It may be cheaper as well.
There is another good reason to get them : Verbatim/Taiyo Yuden media codes tend to be used by drive manufacturers to tune their drives. So those should definitely burn at 8x. If you have some doubts, just get a small amount to try first(e.g. 25pcs).