May have been done before, maybe not. Really like playing this character. I'm the only build like it on my PW, so it is very fun. Does decent damage, but is weaker at lower levels. The reason I like it is you can use the high charisma bonus of the bard levels to full extent. The character has good melee stats and a very high charisma. I played this char with a longsowrd and shield, but you could do more damage if you had a big weapon. The PW i play on is rather low magic so AC is important, hence why I chose the shield.
Final class progression would be bard 26/Blackguard 4/RDD 10. Starting stats: Human str 16 dex 12 con 14 int 8 wis 8 cha 16
Looking back may have been better to lower str to 14 and int to 12, however i am not sure how that would affect the aquisition of dev crit. Still should be able to get it, just have to have fewer points into charisma. With 8 int i had trouble gettnig all the skills I wanted.
I took the following classes when building the character. I decided to take the bard levels firt, but you could switch in the RDD levels sooner if needed. I liked the buffs so i went with 16 bard first. Mainly for GMW and the nice bard song, since im on a low magic server. Also you get more use out of the divine might feat earlier with the bard's eagle's splendor spell. Potions could replace it if you have potions available on your server in large supply.
With this build you can get dev. crit and get good use out of the divine might and divine shield feats.
Final Stats were as follows:
26 str 12 dex 16 con 10 int 8 wis 32 cha
Skill points are rough for this character with a low intelligence, and I had to forgoe spellcraft and much of UMD to keep tumble, discipline, and perform maxed out. You have to spend some skillpoints on hide and lore for the RDD so in early levels you may not be able to keep al those skills maxed. If you start with 14 str and 12 int you shuld be able to spend a couple points on str instad of charisma and get the feats as well. Your charisma wont be as high however. Possibly 28-30.
I also did this build without focusing on Dev. Crit. and got the charisma unbuffed up to 37. Saves were higher on this one, as was the damage and AC from divine might/shield, however you dont get dev. crit. From a roleplay prespective, I like the higher charisma build better, but Dev. Crit is quite nice.
Feats Taken (from memory): Power attack (1) Cleave (1) Extra Music (3) Great Cleave (6) Curse Song (9) Divine Might (12) Divine Shield (15) Improved Critical (Longsword/Greatsword) (18) Great Charisma (21) Great Charisma (24) Great Charisma (27) Weapon Focus (Longsword) (30) Overwhelming Critical (33) Devastating Critical (36) Great Charisma (39)
The bard bonus feats I got I believe I used great charisma. You could probably get Dev. Crit three levels earlier if you substitute Great Charisma at lvl 27 for Great Strength and put the ability increase at level 28 into strength, however that will make your total charisma lower. Its up to you. You final strength score would be about 28 then.
Keep in mind with this build you can get +10 str through spells for a short time (bard and BG bulls str stack) and +5 charisma through spells. Bard song bonuses and bard spell bonuses like warcry and GMW if you are on a low magic world. I wore full plate with this character. You'll just have to buff before combant. Curse song is a help as well and it certainly fits the character if you are wishing to roleplay it more.
EDIT: For stat increases focus primarily on charisma. I put one point into strength at level 20 (to enble dev crit from only the str increases from RDD prc) and one into strength at level 40 (to make str even 26 and cha even 32).