Interestingly, I couldn't think of an answer to your specific question about the past participle of stride. Perhaps this is because I couldn't think of a natural situation in which I might use this verb in the present perfect. This thought was reinforced when I found that the Oxford Advanced Learner's Dictionary does not list a past participle in its appendix of irregular verbs. In the main dictionary entry for 'stride' it says: not used in the perfect tenses.
The Concise Oxford Dictionary gives stridden.
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