Do acronyms borrowed from English use neutral tone (aka tone 0 or tone 5) for all syllables?
In short: the standard pronunciation is the English pronunciation.

There's no Chinese standard way to pronounce English letter (how they are pronounced when they are used as pinyin should not be counted here, I think). Tone does not exist for English letters, as they are English, not Chinese. English intonation should take effect(in English, when 'DVD' is pronounced, some letter would be falling, others not).

However, as only few can pronounce English very good in China, and as the pronunciation is affected by the whole sentence(which is in Chinese), what mostly used is in fact Chinglish.

And the pinyin 'sìdì' for CD in wikitionary is definitely wrong. I've never heard anybody talk like that. Pinyin cannot be assigned to English letters.